Liquid crystal panel and equipment comprising said liquid crystal panel

ABSTRACT

Non-uniformity of a cell gap of a liquid crystal panel is suppressed from affecting display adversely. Concentric interference fringes are unavoidably formed in a liquid crystal cell in which liquid crystal is sealed and the cell gap is maintained by a sealing member without using scattered spacers. Then, peripheral driving circuits are provided in regions where the interference fringes exist and a pixel matrix circuit is disposed in a region where no interference fringe exists. It is then possible to suppress the cell gap from affecting the display by determining the circuit configuration by parameterizing the interference fringes as described above.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed in the present specification relates to a liquidcrystal panel which can display images favorably and to equipments usingsuch liquid crystal panel.

2. Description of Related Art

There has been known an active matrix type liquid crystal display havinga structure in which an active matrix circuit, a circuit for driving theactive matrix circuit (referred to as a peripheral driving circuit) andother peripheral circuits (various circuits required for a liquidcrystal panel) are integrated on one and the same substrate by TFTs.This structure is called a peripheral driving circuit integrated typeliquid crystal display.

This structure is characterized in that:

(1) the whole construction may be simplified and miniaturized;

(2) its fabrication process may be simplified; and

(3) it is advantageous in lowering power consumption.

Because it is required to reduce the size of the liquid crystal panelused in portable information processing terminals, a projector typeliquid crystal display and the like, it is very useful to integrate theperipheral driving circuit to that end.

According to the finding of the inventors et. al., the existence ofspacers which decide a thickness of a liquid crystal layer causes aproblem in miniaturizing the liquid crystal panel.

For instance, because the size of a pixel is around 30 to 40 μm squareor less in a small liquid crystal panel which is used for a projectorand the like and whose size across corners is less than 2 inches, itsdisplay is influenced by the shadow of the spacers which exist withinthe unit pixel and whose diameter is several μm.

In order to solve such a problem, it is conceivable to arrange so as tomaintain a cell gap (which is defined as corresponding to the thicknessof the liquid crystal layer) by a sealing member (sealant) disposed soas to surround a pixel region (pixel matrix region), without using thespacers.

FIG. 2A schematically shows a transmission type liquid crystal panelwhich has been made in trial to observe a cell gap and whose screen sizeacross corners is 1.4 inches. Because this liquid crystal panel is aprototype, no active matrix circuit nor peripheral driving circuit areformed.

In FIG. 2A, one denoted by the reference numeral 21 is a sealing memberand liquid crystal is filled on the inside thereof. This liquid crystalpanel is arranged such that the cell gap is maintained by a materialcalled filler contained within the sealing member 21 and having apredetermined size.

No spacer for maintaining the cell gap is used in this liquid crystalpanel. That is, no means for maintaining the cell gap is provided exceptof the region where the sealing member is provided.

A liquid crystal injection port 24 is closed by ultraviolet hardeningresin or the like after injecting the liquid crystal. The referencenumeral 23 denotes a glass substrate composing the liquid crystal panel.The figure shows a state in which two glass substrates overlap eachother (the liquid crystal is maintained between these two glasssubstrates).

Because no spacer exists in the pixel region (inside of the sealingmember 21 in this case) in this arrangement, no spacer affects the imagequality.

However, when monochromic light is irradiated to the liquid crystalpanel shown in FIG. 2A, concentric interference fringes 25 are observedfrom the region where the sealing member is provided to the center ofthe liquid crystal panel as shown in FIG. 2B.

The interference fringes 25 indicate that the interval of the cell gapis not uniform. That is, it indicates that the cell gap is narrow at thecenter part of the liquid crystal panel.

FIG. 3 is a schematic diagram wherein this state is stressed extremely.FIG. 3 shows a state in which liquid crystal 22 is interposed andmaintained between a pair of substrates 201 and 202 by the sealingmember 21. It also shows that a cell gap d is small at the center part203 of the liquid crystal panel.

The interference fringes shown in FIG. 2B appear at part 204 where thepositional variation of the cell gap is large. No interference fringeappears at the center part 203 of the liquid crystal cell because thecell gap barely varies there.

The interference fringes as shown in FIG. 2B is caused by interferenceof light reflected from the surface of the substrates composing theliquid crystal cell.

The principle of causing the interference fringes will be explained withreference to FIG. 4. FIG. 4 shows a state in which a pair of glasssubstrates 41 and 42 face each other while keeping the gap (correspondsto the cell gap) thereof inconstant.

When monochromic light 43 is input in such a state, light reflected bythe back face of one glass substrate 41 interferes with light reflectedon the surface of the other glass substrate 42 (although there existsother interferences, it is considered as such in order to simplify thediscussion).

If the cell gap d is constant, i.e. if d₁=d₂=d₃, no bright and darkstripe pattern appears because the state of the interference is the sameat any part.

However, when the gap d is different depending on locations, the brightand dark conditions differ depending on the locations, causing a stripepattern in accordance to the state of changes of the gap d.

The stripe pattern is assumed to be caused when there is a difference ofabout λ/2 in the difference of the cell gap at each location.

When a cell gap at a first bright part is d₁ and a cell gap at aneighboring second bright part is d₂, a difference of an optical pathlength at those two locations is 2(d₂−d₁) considering that the lightreciprocates in the cell gap.

The first and second bright conditions hold when there is a differenceof about a wavelength λ of the incident light 43 between the two opticalpath lengths.

Accordingly, an expression λ=2(d₂−d₁) holds. That is, the difference(d₂-d₁) of the cell gap of the two bright parts is about λ/2.

Because the wavelength λ of the incident light 43 is around 500 to 550nm (0.5 to 0.55 μm) in general, the difference of the cell gaps isestimated to be around 0.25 μm.

Actually, because the state of reflection of light on the surface ofglass is not so simple (it is complicated when an insulating film, aconductive film or the like is formed on the surface of the glasssubstrate) and wavelength of light within a liquid crystal materialturns out to be λ/n by refractive index n of the liquid crystal materialwhen the liquid crystal material is filled therebetween, theabove-mentioned difference of the cell gaps will be smaller than theestimated value.

In any case, the stripe pattern is observed when the cell gap varies inthe order of about several tenth of visual light.

Generally, the cell gap of the liquid crystal panel is set around at 1to 5 μm. This value is decided depending on operation modes or a liquidcrystal material to be used.

However, when the cell gap of the liquid crystal panel deviates by 10%or more from the preset value, transmittancy of light transmittingthrough the liquid crystal changes by around 20% or more of the presetvalue.

Accordingly, when the liquid crystal panel wherein the interferencefringes as shown in FIG. 2B are observed is fabricated by setting thecell gap at 3 μm and the whole of the inside of the sealing member isused as a display screen, a difference of cell gap in the order of μm isproduced between the peripheral part and the center part of the screen.

This means that the state of display might differ remarkably at theperipheral part and the center part of the screen (in fact, a screendisplay whose image quality differs in the shape of donuts is observed).

Accordingly, it is an object of the invention disclosed in the presentspecification to solve the above-mentioned problem of non-uniformity ofthe cell gap in the liquid crystal panel.

SUMMARY OF THE INVENTION

The invention disclosed in the present specification is characterized inthat a liquid crystal panel is constructed by taking in the existence ofinterference fringes as a design parameter by presupposing that theinterference fringes are produced on the face of the liquid crystalpanel when the liquid crystal panel is fabricated.

In concrete, a pixel matrix region is disposed while avoiding a regionwhere the interference fringes are produced and peripheral drivingcircuits are disposed in the region where the interference fringes areproduced.

It allows to prevent the existence of the interference fringes fromaffecting adversely the display even on the liquid crystal panel whichcauses the interference fringes. Further, because it allows the circuitsto be disposed without wasted area within the liquid crystal cell, theequipment may be miniaturized to the minimum.

It is noted that although the region where the peripheral circuits aredisposed is the region where the cell gap varies significantly dependingon locations and there is a fear that it affects adversely the operationof the circuit, the variation of the cell gap in the level of causingthe interference fringes depending on the locations causes no problemunless pressure is directly applied on the peripheral circuit itself.

One of the inventive liquid crystal panel disclosed in the presentspecification is characterized in that liquid crystal is interposed andheld between a pair of substrates; the liquid crystal is sealed within apredetermined region by a sealing member; a thickness of a liquidcrystal layer is maintained by the sealing member; the liquid crystallayer has non-uniformity with respect to its thickness, thus causinginterference fringes; an active matrix circuit is provided in a regionwhere no interference fringe appears; and peripheral circuits areprovided in regions where the interference fringes appear.

The above-mentioned structure is not limited specifically in terms oftypes of liquid crystal material and operation modes.

The interference fringes are what are produced when monochromic light isirradiated to the liquid crystal panel.

The peripheral circuits include a circuit for simply driving the activematrix circuit.

A structure of another inventive liquid crystal panel is characterizedin that liquid crystal is interposed and held between a pair ofsubstrates; the liquid crystal is sealed within a predetermined regionby a sealing member; a thickness of a liquid crystal layer is maintainedby the sealing member; the liquid crystal layer has non-uniformity withrespect to its thickness, thus causing interference fringes; theinterference fringes are shaped concentrically; an active matrix circuitis provided on the inside of regions where the concentric interferencefringes appear; and peripheral circuits are provided in regions wherethe interference fringes appear.

A structure of a still other inventive liquid crystal panel ischaracterized in that liquid crystal is interposed and held between apair of substrates; the liquid crystal is sealed within a predeterminedregion by a sealing member; a thickness of a liquid crystal layer ismaintained by the sealing member; the liquid crystal layer hasnon-uniformity with respect to its thickness, thus causing interferencefringes; the interference fringes are shaped concentrically; an activematrix circuit is provided in a region where no interference fringeappears at the center part of the concentric interference fringes; andperipheral circuits are provided in regions where the interferencefringes appear.

Preferably, each invention described above is applied to one in whichthe thickness of the liquid crystal layer is maintained only by thesealing member. That is, the invention disclosed in the presentspecification is effective especially when no means for maintaining thethickness of the liquid crystal layer is provided on the inside of thesealing member.

It is because concentric interference fringes as indicated by thereference numeral 102 in FIG. 1 are liable to appear specifically insuch a case.

The concentric shape described above means a shape in which a pluralityof graphics having almost the same center and having different sizesexist. It is the state in which a plurality of graphics having anapproximately rectangular shape (whose corners are rounded) as indicatedby the reference numeral 102 in FIG. 1 exist.

The liquid crystal panel may be either a transmission type or reflectiontype liquid crystal panel in the invention disclosed in the presentspecification.

The specific nature of the invention, as well as other objects, uses andadvantages thereof, will clearly appear from the following descriptionand from the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a state wherein a liquid crystalpanel of one embodiment is seen from the top;

FIGS. 2A and 2B are diagrams showing a structure of a liquid crystal;

FIG. 3 is a schematic diagram showing a state of a cell gap of theliquid crystal panel;

FIG. 4 is a diagram illustrating a principle of causing interferencefringes; and

FIGS. 5A through 5F show equipments utilizing the liquid crystal panel.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention disclosed in the present specification is characterized inthat observed interference fringes which are caused by non-uniformity ofcell gap (corresponds to a thickness of a liquid crystal layer) of aliquid crystal panel are taken in as design parameters to utilize it inthe construction of the liquid crystal cell.

In concrete, in the liquid crystal panel as shown in FIG. 1, an activematrix circuit 105 is disposed on the inside of regions whereinterference fringes 102 exist and peripheral circuits are disposed inthe regions where the interference fringes 102 exist.

Thereby, it is possible to prevent the interference fringes 102 fromappearing in the display even if the panel has such a structure ofcausing the interference fringes 102.

This invention is effective especially to the liquid crystal panelhaving a structure in which the thickness of the liquid crystal layer(cell gap) is decided by a sealing member 101 as shown in FIG. 1.

First Embodiment

FIG. 1 shows the scheme (schematic diagram of an upper face) of theliquid crystal panel utilizing the invention disclosed in the presentspecification.

In the arrangement shown in FIG. 1, the reference numeral 101 denotesthe sealing member. The cell gap of the liquid crystal panel shown inFIG. 1 is maintained by a material called filler contained within thesealing member 101. No spherical spacer or the like is used within apixel matrix 105.

Liquid crystal is filled on the inside of the sealing member 101. Aninjection port 106 of the liquid crystal is closed by ultraviolethardening resin in the state shown in the figure.

A pattern 102 of interference fringes appears when visual light isirradiated. What is important in the arrangement shown in FIG. 1 is thatthe pixel matrix region 105 is provided not in the region where thestripe pattern appears but in the region where no stripe pattern exists.

That is, because the region where the interference fringes exist is thelocation where the cell gap varies significantly (the cell gap varies tothe level of influencing the display), it is not used as the screen andperipheral circuits are disposed in the regions where the interferencefringes exist, i.e. in the optically dead space.

In FIG. 1, there are peripheral driving circuits 103 and 104 for drivingthe pixel matrix 105. Because a circuit composed of a shift register, aswitch and a buffer is utilized as the peripheral circuit here, theperipheral circuit will be referred to as a peripheral driving circuit.

The peripheral driving circuits 103 and 104 are provided in the region102 where the stripe pattern is formed. The cell gap varies with adistance of about ½ or less of a wavelength of visual light with respectto the intervals of the stripes in the region where the stripe patternis formed. That is, it varies in the order of about 0.25 μm or less.

This situation may be considered that the thickness of the liquidcrystal layer also varies in the order of about 0.25 μm or less.Accordingly, it may be considered that the thickness of the liquidcrystal layer varies in the order of about 0.25 μm or more in the regionwhere the stripe pattern exists.

Transmittancy of light transmitting through the liquid crystal layervaries considerably depending on the thickness of the liquid crystallayer. The thickness of the liquid crystal layer is changing sharplywhere the stripe pattern is condensed. Accordingly, the transmittancy oflight also varies significantly depending on locations in this region.

In the arrangement shown in FIG. 1, the pixel matrix region is disposedwhile avoiding the region where the thickness of the liquid crystallayer varies significantly (i.e. the region where the stripe pattern isformed).

It allows the influence of the significant changes of the thickness ofthe liquid crystal layer, which varies depending on locations, on thescreen display to be eliminated.

Basically, it is impossible to avoid the stripe pattern as shown by thereference numeral 102 when it is arranged to maintain the cell gap onlyby the sealing member (although there is a method of utilizing a specialglass substrate having a high rigidity, it is expensive and is notpractical).

Accordingly, it is useful to adopt the circuit configuration asillustrated in the present embodiment presupposing that there exists thestate of the cell gap in which the interference fringes 102 areproduced.

Second Embodiment

Equipments comprising the liquid crystal panel utilizing the presentinvention will be exemplified in the present embodiment. Such equipmentsinclude a video camera, a digital still camera, a head-mount display, acar-navigation system, a personal computer and a portable informationterminal (a mobile computer, a portable telephone and the like).

FIG. 5A shows a mobile computer comprising a main body 2001, a camerasection 2002, a receiver section 2003, control switches 2004 and aliquid crystal panel 2005. The type of the liquid crystal panel 2005 maybe either a reflection type or a transmission type.

FIG. 5B shows a head-mount display comprising a main body 2101, areflection type liquid crystal panel 2102 and a band section 2103.

FIG. 5C shows a front projection type liquid crystal panel. Thisequipment is arranged so as to guide light from a light source 2202 to areflection type liquid crystal panel 2203 by an optical system 2204 andto project images optically modulated by the liquid crystal panel 2203to a screen 2205 by enlarging by the optical system 2204. This type ofprojection requires the screen 2205 beside a main body 2201.

FIG. 5D shows a portable telephone comprising a main body 2301, a voiceoutput section 2302, a voice input section 2303, a liquid crystaldisplay 2304, control switches 2305 and an antenna 2306.

FIG. 5E shows a video camera comprising a main body 2401, a liquidcrystal display 2402, a voice input section 2403, control switches 2404,a battery 2405 and a receiver section 2406.

FIG. 5F shows an equipment called a rear-projection type projector. Thisequipment is arranged so as to optically modulate light emitted from alight source 2502 by a polarization beam splitter 2504 on a reflectiontype liquid crystal panel 2503 and to reflect it by reflectors 2505 and2506 to project to a screen 2507. The screen 2507 is disposed within amain body 2502 in this type of equipment.

Accordingly, it is possible to provide the liquid crystal panel in whichthe influence of the non-uniformity of the cell gap will not appear inthe display even if it exists by utilizing the invention disclosed inthe present specification.

While the preferred embodiments have been described, variations theretowill occur to those skilled in the art within the scope of the presentinventive concepts which are delineated by the following claims.

1. A display device comprising: a liquid crystal panel comprising: afirst substrate and a second substrate opposed to each other, and havinga gap therebetween; a pixel region and a driving circuit, each of thepixel region and the driving circuit comprising thin film transistors; aliquid crystal material between the first and second substrates; and asealing member between the first and second substrates to maintain theliquid crystal material between the first and second substrates, whereinan interference fringes appear where the gap varies in an order of 0.25μm or more, wherein the driving circuit is provided in a region wherethe interference fringes appear, and wherein the pixel region isprovided outside the region.
 2. A display device according to claim 1,wherein the liquid crystal panel is a transmission type liquid crystalpanel.
 3. A display device according to claim 1, wherein the liquidcrystal panel is a reflection type liquid crystal panel.
 4. A displaydevice according to claim 1, wherein the gap is from 1 to 5 μm.
 5. Adisplay device according to claim 1, wherein the display device isincorporated in at least one selected from the group consisting of amobile computer, a head-mount display, a video camera, a projector and aportable telephone.
 6. A display device comprising: a liquid crystalpanel comprising: a first substrate and a second substrate opposed toeach other, and having a gap therebetween; a pixel region and a drivingcircuit, each of the pixel region and the driving circuit comprisingthin film transistors; a liquid crystal material between the first andsecond substrates; and a sealing member between the first and secondsubstrates to maintain the liquid crystal material between the first andsecond substrates, wherein an interference fringes appear where the gapvaries in an order of 0.25 μm or more, wherein the driving circuit isprovided in a region where the interference fringes appear, wherein thepixel region is provided outside the region, and wherein the liquidcrystal panel has no spacer between the first and second substrates. 7.A display device according to claim 6, wherein the liquid crystal panelis a transmission type liquid crystal panel.
 8. A display deviceaccording to claim 6, wherein the liquid crystal panel is a reflectiontype liquid crystal panel.
 9. A display device according to claim 6,wherein the gap is from 1 to 5 μm.
 10. A display device according toclaim 6, wherein the display device is incorporated in at least oneselected from the group consisting of a mobile computer, a head-mountdisplay, a video camera, a projector and a portable telephone.
 11. Adisplay device comprising: a liquid crystal panel comprising: a firstsubstrate and a second substrate opposed to each other, and having a gaptherebetween; a pixel region and a driving circuit, each of the pixelregion and the driving circuit comprising thin film transistors; aliquid crystal material between the first and second substrates; and asealing member between the first and second substrates to maintain theliquid crystal material between the first and second substrates, whereinan interference fringes appear where the gap varies in an order of 0.25μm or more, wherein the driving circuit is provided in a region wherethe interference fringes appear, wherein the pixel region is providedoutside the region, and wherein the liquid crystal panel has an acrosscorners size of less than 2 inches.
 12. A display device according toclaim 11, wherein the liquid crystal panel is a transmission type liquidcrystal panel.
 13. A display device according to claim 11, wherein theliquid crystal panel is a reflection type liquid crystal panel.
 14. Adisplay device according to claim 11, wherein the gap is from 1 to 5 μm.15. A display device according to claim 11, wherein the display deviceis incorporated in at least one selected from the group consisting of amobile computer, a head-mount display, a video camera, a projector and aportable telephone.
 16. A display device comprising: a liquid crystalpanel comprising: a first substrate and a second substrate opposed toeach other, and having a gap therebetween; a pixel region and a drivingcircuit, each of the pixel region and the driving circuit comprisingthin film transistors; a liquid crystal material between the first andsecond substrates; and a sealing member between the first and secondsubstrates to maintain the liquid crystal material between the first andsecond substrates, wherein an interference fringes appear where the gapvaries in an order of 0.25 μm or more, wherein the driving circuit isprovided in a region where the interference fringes appear, wherein thepixel region is provided outside the region, and wherein the liquidcrystal panel has no spacer between the first and second substrates, andhas an across corners size of less than 2 inches.
 17. A display deviceaccording to claim 16, wherein the liquid crystal panel is atransmission type liquid crystal panel.
 18. A display device accordingto claim 16, wherein the liquid crystal panel is a reflection typeliquid crystal panel.
 19. A display device according to claim 16,wherein the gap is from 1 to 5 μm.
 20. A display device according toclaim 16, wherein the display device is incorporated in at least oneselected from the group consisting of a mobile computer, a head-mountdisplay, a video camera, a projector and a portable telephone.